Dry Eye Syndrome, or Keratoconjunctivitis Sicca (KCS) is one of the most frequently established diagnoses in ophthalmology. Current estimates hold that roughly 40-60 million people in the United States exhibit dry eye symptoms. The lack of accurate statistical data about the occurrence of dry eye is due largely to a lack of state-of-the-art diagnostic equipment. A more disturbing trend, however, is the misdiagnosis of dry eye or its escape from early detection altogether, since symptomatic patients are not always easily identified.
Pursuing more effective diagnosis will strengthen the paradigm of ophthalmic care available in this country. The pharmaceutical industry recognizes this. The first prescription pharmaceuticals for treating dry eye are now appearing on the market, with more on the way in the next twenty-four months, and yet the methods for diagnosis and monitoring treatment remain problematic.
There is no ‘gold standard’ test that both diagnoses dry eye and monitors the effect of its treatment. The popular method is a matrix of subjective observation of symptoms and objective tests (such as Schirmer testing, staining techniques and tear break-up time) none of which is specific to the detection of dry eye or the measurement of its severity.
Considering recent pharmaceutical advancements aimed at treating dry eye, timely and parallel advancements in diagnostic technologies are needed.
The osmolarity of a tear—the degree of dissolved solids therein—is popularly accepted by experts in the field as an indicator of the presence and severity of dry eye. The instrument most commonly associated with the measurement of tear osmolarity is the osmometer; however, technical limitations have restricted the use of tear osmometers to primarily research environments.
An osmometer is a device that measures the concentration of dissolved solutes in water. Though it is widely used in other fields, osmometers are used in medicine in applications such as determining osmol gap in toxicology and trauma cases, monitoring mannitol treatment infusions, monitoring the absorption in Glycine ingestion with irrigation fluids in surgical procedures, among others.
Despite the suitability of this technology for measuring tear osmolarity, the current devices present certain limitations that prevent their widespread use in a clinical environment. The most prevalent problem has to do with sample size.
Nearly all commercially available osmometers are designed (and perhaps technologically limited) to measure milliliter-size samples. Tear samples extracted from patients tend to be in the nanoliter volumes and further complicating matters, dry eye patients generally have less tears and make handling samples even more difficult. The only osmometer designed to measure nanoliter sample sizes, is no longer available commercially and is too cumbersome for practical use in a clinical environment. The result is that practicing ophthalmologists are left with a haphazard methodology and inadequate tools to accurately detect this prevalent condition.